2012年10月16日星期二

Good Way to Understand Aperture

Aperture is one of the three pillars of
photography, the other two being ISO and Shutter Speed. Without
a doubt, it is the most talked about subject, because aperture either adds a
dimension to a photograph by blurring the background, or magically brings
everything in focus.

1) What is Aperture?

Aperture is a hole within a lens, through
which light travels into the camera body. Take our eyes as example. The cornea
in our eyes is like the front element of a lens – it gathers all external
light, then bends it and passes it to the iris. Depending on the amount of
light, the iris can either expand or shrink, controlling the size of the pupil,
which is a hole that lets the light pass further into the eye. The pupil is
essentially what we refer to as aperture in photography. The amount
of light that enters the retina (which works just like the camera sensor), is
limited to the size of the pupil – the larger the pupil, the more light enters
the retina.

2) Size of Aperture – Large vs Small
Aperture

In photography, aperture is expressed in
f-numbers (for example f/5.6). These f-numbers that are known as “f-stops” are
a way of describing the size of the aperture, or how open or closed the
aperture is. A smaller f-stop means a larger aperture, while a larger f-stop
means a smaller aperture. Most people find this awkward, since we are used to
having larger numbers represent larger values, but not in this case. For
example, f/1.4 is larger than f/2.0.

Take a look at this chart: The larger the
f-number, the smaller the aperture.

3) What
is Depth of Field?

The
size of the aperture has a direct impact on the depth of field, which is
the area of the image that appears sharp. A large f-number such as f/32, (which
means a smaller aperture) will bring all foreground and background objects in
focus, while a small f-number such as f/1.4 will isolate the foreground from
the background by making the foreground objects sharp and the background blurry.